1. Field of the Invention
This invention relates to an anti-backlash nut for engaging a lead screw.
2. Description of the Relevant Art
The use of lead screw mechanisms for providing linear motion is well known. A typical lead screw mechanism has a rotating lead screw and a non-rotating traveler that is coupled to the lead screw with a nut. The traveler is typically guided or constrained so that rotation of the lead screw results in linear motion of the traveler.
Fairly high precision positioning can be accomplished with a lead screw mechanism by accurately controlling the rotation of the lead screw. An essential component for precision positioning is an anti-backlash nut or other coupling between the lead screw shaft and the traveler, which reduces or, ideally, eliminates positioning hysteresis resulting from bidirectional rotation of the lead screw.
There are tradeoffs in the design of anti-backlash nuts in that a greater precision (less backlash) may be achieved by reducing the clearance and increasing the contact area and/or forces between the lead screw and the anti-backlash nut, but at the expense of higher frictional forces and wear. It is desirable to have the nut apply a uniform pressure to the lead screw so that there is the same torque load on the lead screw regardless of the direction of travel. It is desirable to have a torsionally stiff nut that avoids or minimizes any wind-up or torsional distortion that could cause positioning inaccuracies. It is desirable to be able to adjust the pressure applied by the nut to optimize it for a particular application. It is also desirable to provide some float or compliance in the nut to avoid binding or high torque, but at the same time not compromising positioning accuracy.